The present invention generally relates to an atrial defibrillator and method for applying cardioverting electrical energy to the atria of a human heart in need of cardioversion. The present invention is more particularly directed to an improved atrial fibrillation detection system and method for use in an implantable atrial defibrillator wherein cardiac activity detected in an atrial channel during selected portions of a plurality of cardiac cycles is analyzed for determining if the atria are in fibrillation. More specifically, the atrial fibrillation detection system and method of the present invention contemplates counting cardiac events detected in the atrial channel during the selected portions of the plurality of cardiac cycles and determining if the atria are in fibrillation responsive to the number of cardiac events counted.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life-threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected ventricular electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality. Two such proposed defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator from external to the patient's skin with a magnet.
In order for an implantable atrial defibrillator to be truly automatic, it must include an atrial fibrillation detector which, responsive to monitored activity of the heart, determines if the atria are in fibrillation. While numerous atrial fibrillation detection methods have been proposed in the past, they all generally contemplate the processing of rather complex algorithms. Such algorithms require extensive computational resources and generally take a significant amount of time to complete. The end result is that prior art atrial fibrillation detectors consume a significant amount of power. Since implantable atrial defibrillators are powered by a depletable power source, such as a battery, the predicted lifetime of an implantable atrial defibrillator can be greatly influenced by the amount of power consumed by its atrial fibrillation detector.
Hence, there is a need in the art for an improved atrial fibrillation detector which consumes little power during the detection of atrial fibrillation. Such an atrial fibrillation detector should require minimal computational resources and be able to complete its analysis in a short period of time. The present invention provides an atrial fibrillation detection system and method which consumes little power by requiring minimal computational resources and by being able to complete atrial fibrillation analysis in a short period of time.